There are conventional macro lens systems having close distance imaging at imaging magnification ratios of approximately 1× as their main purpose.
These macro lens systems are capable of continuously focusing when imaging an object at infinity to an object at a most proximate distance at which the imaging magnification ratio is approximately 1×. The macro lens systems are particularly designed to obtain high optical performance during imaging of objects at close distances.
Generally, the floating focus method, in which two or more lens groups are moved during focusing operations, is employed in order to suppress variations in aberration accompanying the focusing operations.
Conventionally, the front focusing type of focusing operation, in which the lens group most toward the object side is driven forward, had been utilized. However, in the case that an object at a most proximate distance is imaged, the lens will approach the object, and therefore operability deteriorates. In addition, in the case that a first lens group having a large diameter is moved, high speed focusing becomes difficult because the weight of the first lens group is great. In addition, there was a problem that in the case that close distance imaging at approximately 1× magnification is performed, longitudinal chromatic aberrations become great.
Recently, imaging lenses that adopt the floating focus method, in which a first lens group is fixed and focusing operations are performed by moving a plurality of other lens groups, are being employed. Further, focusing methods that move three or more lens groups in order to further suppress variations in aberration due to focusing operations have been proposed in Japanese Unexamined Patent Publication Nos. 2012-058682 and 2011-048232.